This invention relates to an apparatus for purifying and liquifying natural gas.
When longwall mining techniques are used, large volumes of mine gas containing natural gas and air are released as the overburden collapses behind the advancing mining machinery. The practice has been to drill holes from the surface and siphon off the gas through these holes. When this gas is so disposed of, large volumes of potentially useful natural gas are destroyed. Prior art gas liquifiers have not been of the self-contained and portable nature necessary for easy transportation to the mine or other location where it is desired to liquify gas.
One reason for this has been the relatively complex system of valving and piping used to change the molecular sieve assemblies from the cleaning mode to the regenerating mode. This may be seen in U.S. Pat. No. 3,087,291 to Jackson where six valves are used for changing the modes of operation of two seive assemblies of a gas purifying apparatus.
Another problem involves providing a suitable source for gas to heat and cool the molecular sieve assemblies during regeneration. In some liquifying apparatuses, natural gas has been burned to heat the gas for heating the sieve assemblies. However, this cannot be safely done near the liquifying apparatus itself. Consequently, the heater must be placed a distance away from the liquifying apparatus and this prevents the apparatus from being packaged in a self-contained unit. One solution to the problem has been to heat the regeneration gas with exhaust gases from motors used to power compressors of the liquifying apparatus. For example, this may be seen in U.S. Pat. Nos. 3,894,856 and 3,780,534 to Lafredo.
If natural gas is used to regenerate the sieve assemblies, and if the gas contains even a trace of air, the sieve assemblies cannot be regenerated properly. If the gas or sieve assemblies are at a temperature above 400.degree. F., catalytic burning of the air and natural gas results, producing carbon dioxide and water to contaminate the molecular sieve assemblies. One solution to this problem is to provide a high degree of separation between the air and natural gas from the original input gas. However, this requires a relatively large and complex separation tower to provide the high degree of separation.
Other patents which may be considered relevant to this invention are U.S. Pat. No. 3,554,904 to Humphries, U.S. Pat. No. 2,704,274 to Allison and U.S. Pat. No. 3,680,944 to Knapp.